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TELNET(1)                 BSD General Commands Manual                TELNET(1)

NAME
     telnet - user interface to the TELNET protocol

SYNOPSIS
     telnet [-8EFKLacdfrx] [-X authtype] [-b hostalias] [-e escapechar] [-k realm] [-l user] [-n tracefile] [host
            [port]]

DESCRIPTION
     The telnet command is used to communicate with another host using the TELNET protocol.  If telnet is invoked
     without the host argument, it enters command mode, indicated by its prompt (telnet>).  In this mode, it accepts
     and executes the commands listed below.  If it is invoked with arguments, it performs an open command with those
     arguments.

     The options are as follows:

     -7      Strip 8th bit on input and output. Telnet is 8-bit clean by default but doesn't send the TELNET BINARY
             option unless forced.

     -8      Specifies an 8-bit data path.  This causes an attempt to negotiate the TELNET BINARY option on both input
             and output.

     -E      Stops any character from being recognized as an escape character.

     -F      If Kerberos V5 authentication is being used, the -F option allows the local credentials to be forwarded
             to the remote system, including any credentials that have already been forwarded into the local environ-
             ment.

     -K      Specifies no automatic login to the remote system.

     -L      Specifies an 8-bit data path on output.  This causes the BINARY option to be negotiated on output.

     -X atype
             Disables the atype type of authentication.

     -a      Attempt automatic login.  Currently, this sends the user name via the USER variable of the ENVIRON option
             if supported by the remote system.  The name used is that of the current user as returned by getlogin(2)
             if it agrees with the current user ID, otherwise it is the name associated with the user ID.

     -b hostalias
             Uses bind(2) on the local socket to bind it to an aliased address (see ifconfig(8) and the ''alias''
             specifier) or to the address of another interface than the one naturally chosen by connect(2).  This can
             be useful when connecting to services which use IP addresses for authentication and reconfiguration of
             the server is undesirable (or impossible).

     -c      Disables the reading of the user's .telnetrc file.  (See the toggle skiprc command on this man page.)

     -d      Sets the initial value of the debug toggle to TRUE.

     -e escapechar
             Sets the initial telnet escape character to escapechar.  If escapechar is omitted, then there will be no
             escape character.

     -f      If Kerberos V5 authentication is being used, the -f option allows the local credentials to be forwarded
             to the remote system.

     -k realm
             If Kerberos authentication is being used, the -k option requests that telnet obtain tickets for the
             remote host in realm realm instead of the remote host's realm, as determined by krb_realmofhost(3).

     -l user
             When connecting to the remote system, if the remote system understands the ENVIRON option, then user will
             be sent to the remote system as the value for the variable USER.  This option implies the -a option.
             This option may also be used with the open command.

     -n tracefile
             Opens tracefile for recording trace information.  See the set tracefile command below.

     -r      Specifies a user interface similar to rlogin(1).  In this mode, the escape character is set to the tilde
             (~) character, unless modified by the -e option.

     -x      Turns on encryption of the data stream if possible.

     host    Indicates the official name, an alias, or the Internet address of a remote host.

     port    Indicates a port number (address of an application).  If a number is not specified, the default telnet
             port is used.

     When in rlogin mode, a line of the form ~.  disconnects from the remote host; ~ is the telnet escape character.
     Similarly, the line ~^Z suspends the telnet session.  The line ~^] escapes to the normal telnet escape prompt.

     Once a connection has been opened, telnet will attempt to enable the TELNET LINEMODE option.  If this fails,
     telnet will revert to one of two input modes: either ''character at a time'' or ''old line by line'' depending on
     what the remote system supports.

     When LINEMODE is enabled, character processing is done on the local system, under the control of the remote sys-
     tem.  When input editing or character echoing is to be disabled, the remote system will relay that information.
     The remote system will also relay changes to any special characters that happen on the remote system, so that
     they can take effect on the local system.

     In ''character at a time'' mode, most text typed is immediately sent to the remote host for processing.

     In ''old line by line'' mode, all text is echoed locally, and (normally) only completed lines are sent to the
     remote host.  The ''local echo character'' (initially ''^E'') may be used to turn off and on the local echo (this
     would mostly be used to enter passwords without the password being echoed).

     If the LINEMODE option is enabled, or if the localchars toggle is TRUE (the default for ''old line by line''; see
     below), the user's quit, intr, and flush characters are trapped locally, and sent as TELNET protocol sequences to
     the remote side.  If LINEMODE has ever been enabled, then the user's susp and eof are also sent as TELNET proto-
     col sequences, and quit is sent as a TELNET ABORT instead of BREAK.  There are options (see toggle autoflush and
     toggle autosynch below) which cause this action to flush subsequent output to the terminal (until the remote host
     acknowledges the TELNET sequence) and flush previous terminal input (in the case of quit and intr).

     While connected to a remote host, telnet command mode may be entered by typing the telnet ''escape character''
     (initially ''^]'').  When in command mode, the normal terminal editing conventions are available.  Note that the
     escape character will return to the command mode of the initial invocation of telnet that has the controlling
     terminal.  Use the send escape command to switch to command mode in subsequent telnet processes on remote hosts.

     The following telnet commands are available.  Only enough of each command to uniquely identify it need be typed
     (this is also true for arguments to the mode, set, toggle, unset, slc, environ, and display commands).

     auth argument [...]
                The auth command manipulates the information sent through the TELNET AUTHENTICATE option.  Valid argu-
                ments for the auth command are as follows:

                disable type  Disables the specified type of authentication.  To obtain a list of available types, use
                              the auth disable ? command.

                enable type   Enables the specified type of authentication.  To obtain a list of available types, use
                              the auth enable ? command.

                status        Lists the current status of the various types of authentication.

     close      Close a TELNET session and return to command mode.

     display argument [...]
                Displays all, or some, of the set and toggle values (see below).

     encrypt argument [...]
                The encrypt command manipulates the information sent through the TELNET ENCRYPT option.

                Valid arguments for the encrypt command are as follows:

                disable type [input|output]
                              Disables the specified type of encryption.  If you omit input and output, both input and
                              output are disabled.  To obtain a list of available types, use the encrypt disable ?
                              command.

                enable type [input|output]
                              Enables the specified type of encryption.  If you omit input and output, both input and
                              output are enabled.  To obtain a list of available types, use the encrypt enable ? com-
                              mand.

                input         This is the same as the encrypt start input command.

                -input        This is the same as the encrypt stop input command.

                output        This is the same as the encrypt start output command.

                -output       This is the same as the encrypt stop output command.

                start [input|output]
                              Attempts to start encryption.  If you omit input and output, both input and output are
                              enabled.  To obtain a list of available types, use the encrypt enable ? command.

                status        Lists the current status of encryption.

                stop [input|output]
                              Stops encryption.  If you omit input and output, encryption is on both input and output.

                type type     Sets the default type of encryption to be used with later encrypt start or encrypt stop
                              commands.

     environ arguments [...]
                The environ command is used to manipulate the variables that may be sent through the TELNET ENVIRON
                option.  The initial set of variables is taken from the users environment, with only the DISPLAY and
                PRINTER variables being exported by default.  The USER variable is also exported if the -a or -l
                options are used.
                Valid arguments for the environ command are:

                define variable value
                            Define the variable variable to have a value of value.  Any variables defined by this com-
                            mand are automatically exported.  The value may be enclosed in single or double quotes so
                            that tabs and spaces may be included.

                undefine variable
                            Remove variable from the list of environment variables.

                export variable
                            Mark the variable variable to be exported to the remote side.

                unexport variable
                            Mark the variable variable to not be exported unless explicitly asked for by the remote
                            side.

                list        List the current set of environment variables.  Those marked with a * will be sent auto-
                            matically, other variables will only be sent if explicitly requested.

                ?           Prints out help information for the environ command.

     logout     Sends the TELNET LOGOUT option to the remote side.  This command is similar to a close command; how-
                ever, if the remote side does not support the LOGOUT option, nothing happens.  If, however, the remote
                side does support the LOGOUT option, this command should cause the remote side to close the TELNET
                connection.  If the remote side also supports the concept of suspending a user's session for later
                reattachment, the logout argument indicates that you should terminate the session immediately.

     mode type  type is one of several options, depending on the state of the TELNET session.  The remote host is
                asked for permission to go into the requested mode.  If the remote host is capable of entering that
                mode, the requested mode will be entered.

                character     Disable the TELNET LINEMODE option, or, if the remote side does not understand the
                              LINEMODE option, then enter ''character at a time'' mode.

                line          Enable the TELNET LINEMODE option, or, if the remote side does not understand the
                              LINEMODE option, then attempt to enter ''old-line-by-line'' mode.

                isig (-isig)  Attempt to enable (disable) the TRAPSIG mode of the LINEMODE option.  This requires that
                              the LINEMODE option be enabled.

                edit (-edit)  Attempt to enable (disable) the EDIT mode of the LINEMODE option.  This requires that
                              the LINEMODE option be enabled.

                softtabs (-softtabs)
                              Attempt to enable (disable) the SOFT_TAB mode of the LINEMODE option.  This requires
                              that the LINEMODE option be enabled.

                litecho (-litecho)
                              Attempt to enable (disable) the LIT_ECHO mode of the LINEMODE option.  This requires
                              that the LINEMODE option be enabled.

                ?             Prints out help information for the mode command.

     open host [-l user] [[-] port]
                Open a connection to the named host.  If no port number is specified, telnet will attempt to contact a
                TELNET server at the default port.  The host specification may be either a host name (see hosts(5)) or
                an Internet address specified in the ''dot notation'' (see inet(3)).  The -l option may be used to
                specify the user name to be passed to the remote system via the ENVIRON option.  When connecting to a
                non-standard port, telnet omits any automatic initiation of TELNET options.  When the port number is
                preceded by a minus sign, the initial option negotiation is done.  After establishing a connection,
                the file .telnetrc in the user's home directory is opened.  Lines beginning with a ''#'' are comment
                lines.  Blank lines are ignored.  Lines that begin without whitespace are the start of a machine
                entry.  The first thing on the line is the name of the machine that is being connected to.  The rest
                of the line, and successive lines that begin with whitespace are assumed to be telnet commands and are
                processed as if they had been typed in manually to the telnet command prompt.

     quit       Close any open TELNET session and exit telnet.  An end-of-file (in command mode) will also close a
                session and exit.

     send arguments
                Sends one or more special character sequences to the remote host.  The following are the arguments
                which may be specified (more than one argument may be specified at a time):

                abort   Sends the TELNET ABORT (Abort processes) sequence.

                ao      Sends the TELNET AO (Abort Output) sequence, which should cause the remote system to flush all
                        output from the remote system to the user's terminal.

                ayt     Sends the TELNET AYT (Are You There) sequence, to which the remote system may or may not
                        choose to respond.

                brk     Sends the TELNET BRK (Break) sequence, which may have significance to the remote system.

                ec      Sends the TELNET EC (Erase Character) sequence, which should cause the remote system to erase
                        the last character entered.

                el      Sends the TELNET EL (Erase Line) sequence, which should cause the remote system to erase the
                        line currently being entered.

                eof     Sends the TELNET EOF (End Of File) sequence.

                eor     Sends the TELNET EOR (End of Record) sequence.

                escape  Sends the current telnet escape character (initially ''^]'').

                ga      Sends the TELNET GA (Go Ahead) sequence, which likely has no significance to the remote sys-
                        tem.

                getstatus
                        If the remote side supports the TELNET STATUS command, getstatus will send the subnegotiation
                        to request that the server send its current option status.

                ip      Sends the TELNET IP (Interrupt Process) sequence, which should cause the remote system to
                        abort the currently running process.

                nop     Sends the TELNET NOP (No OPeration) sequence.

                susp    Sends the TELNET SUSP (SUSPend process) sequence.

                synch   Sends the TELNET SYNCH sequence.  This sequence causes the remote system to discard all previ-
                        ously typed (but not yet read) input.  This sequence is sent as TCP urgent data (and may not
                        work if the remote system is a 4.2BSD system -- if it doesn't work, a lower case ''r'' may be
                        echoed on the terminal).

                do cmd  Sends the TELNET DO cmd sequence.  cmd can be either a decimal number between 0 and 255, or a
                        symbolic name for a specific TELNET command.  cmd can also be either help or ? to print out
                        help information, including a list of known symbolic names.

                dont cmd
                        Sends the TELNET DONT cmd sequence.  cmd can be either a decimal number between 0 and 255, or
                        a symbolic name for a specific TELNET command.  cmd can also be either help or ? to print out
                        help information, including a list of known symbolic names.

                will cmd
                        Sends the TELNET WILL cmd sequence.  cmd can be either a decimal number between 0 and 255, or
                        a symbolic name for a specific TELNET command.  cmd can also be either help or ? to print out
                        help information, including a list of known symbolic names.

                wont cmd
                        Sends the TELNET WONT cmd sequence.  cmd can be either a decimal number between 0 and 255, or
                        a symbolic name for a specific TELNET command.  cmd can also be either help or ? to print out
                        help information, including a list of known symbolic names.

                ?       Prints out help information for the send command.

     set argument value

     unset argument value
                The set command will set any one of a number of telnet variables to a specific value or to TRUE.  The
                special value off turns off the function associated with the variable; this is equivalent to using the
                unset command.  The unset command will disable or set to FALSE any of the specified functions.  The
                values of variables may be interrogated with the display command.  The variables which may be set or
                unset, but not toggled, are listed here.  In addition, any of the variables for the toggle command may
                be explicitly set or unset using the set and unset commands.

                ayt     If TELNET is in localchars mode, or LINEMODE is enabled, and the status character is typed, a
                        TELNET AYT sequence (see send ayt preceding) is sent to the remote host.  The initial value
                        for the "Are You There" character is the terminal's status character.

                echo    This is the value (initially ''^E'') which, when in ''line by line'' mode, toggles between
                        doing local echoing of entered characters (for normal processing), and suppressing echoing of
                        entered characters (for entering, say, a password).

                eof     If telnet is operating in LINEMODE or ''old line by line'' mode, entering this character as
                        the first character on a line will cause this character to be sent to the remote system.  The
                        initial value of the eof character is taken to be the terminal's eof character.

                erase   If telnet is in localchars mode (see toggle localchars below), and if telnet is operating in
                        ''character at a time'' mode, then when this character is typed, a TELNET EC sequence (see
                        send ec above) is sent to the remote system.  The initial value for the erase character is
                        taken to be the terminal's erase character.

                escape  This is the telnet escape character (initially ''^['') which causes entry into telnet command
                        mode (when connected to a remote system).

                flushoutput
                        If telnet is in localchars mode (see toggle localchars below) and the flushoutput character is
                        typed, a TELNET AO sequence (see send ao above) is sent to the remote host.  The initial value
                        for the flush character is taken to be the terminal's flush character.

                forw1

                forw2   If TELNET is operating in LINEMODE, these are the characters that, when typed, cause partial
                        lines to be forwarded to the remote system.  The initial value for the forwarding characters
                        are taken from the terminal's eol and eol2 characters.

                interrupt
                        If telnet is in localchars mode (see toggle localchars below) and the interrupt character is
                        typed, a TELNET IP sequence (see send ip above) is sent to the remote host.  The initial value
                        for the interrupt character is taken to be the terminal's intr character.

                kill    If telnet is in localchars mode (see toggle localchars below), and if telnet is operating in
                        ''character at a time'' mode, then when this character is typed, a TELNET EL sequence (see
                        send el above) is sent to the remote system.  The initial value for the kill character is
                        taken to be the terminal's kill character.

                lnext   If telnet is operating in LINEMODE or ''old line by line'' mode, then this character is taken
                        to be the terminal's lnext character.  The initial value for the lnext character is taken to
                        be the terminal's lnext character.

                quit    If telnet is in localchars mode (see toggle localchars below) and the quit character is typed,
                        a TELNET BRK sequence (see send brk above) is sent to the remote host.  The initial value for
                        the quit character is taken to be the terminal's quit character.

                reprint
                        If telnet is operating in LINEMODE or old line by line'' mode, then this character is taken to
                        be the terminal's reprint character.  The initial value for the reprint character is taken to
                        be the terminal's reprint character.

                rlogin  This is the rlogin escape character.  If set, the normal TELNET escape character is ignored
                        unless it is preceded by this character at the beginning of a line.  This character, at the
                        beginning of a line, followed by a "." closes the connection; when followed by a ^Z it sus-
                        pends the telnet command.  The initial state is to disable the rlogin escape character.

                start   If the TELNET TOGGLE-FLOW-CONTROL option has been enabled, then this character is taken to be
                        the terminal's start character.  The initial value for the start character is taken to be the
                        terminal's start character.

                stop    If the TELNET TOGGLE-FLOW-CONTROL option has been enabled, then this character is taken to be
                        the terminal's stop character.  The initial value for the stop character is taken to be the
                        terminal's stop character.

                susp    If telnet is in localchars mode, or LINEMODE is enabled, and the suspend character is typed, a
                        TELNET SUSP sequence (see send susp above) is sent to the remote host.  The initial value for
                        the suspend character is taken to be the terminal's suspend character.

                tracefile
                        This is the file to which the output, caused by netdata or option tracing being TRUE, will be
                        written.  If it is set to "-", then tracing information will be written to standard output
                        (the default).

                worderase
                        If telnet is operating in LINEMODE or ''old line by line'' mode, then this character is taken
                        to be the terminal's worderase character.  The initial value for the worderase character is
                        taken to be the terminal's worderase character.

                ?       Displays the legal set (unset) commands.

     skey sequence challenge
                The skey command computes a response to the S/Key challenge.  See skey(1) for more information on the
                S/Key system.

     slc state  The slc command (Set Local Characters) is used to set or change the state of the special characters
                when the TELNET LINEMODE option has been enabled.  Special characters are characters that get mapped
                to TELNET commands sequences (like ip or quit) or line editing characters (like erase and kill).  By
                default, the local special characters are exported.

                check       Verify the current settings for the current special characters.  The remote side is
                            requested to send all the current special character settings, and if there are any dis-
                            crepancies with the local side, the local side will switch to the remote value.

                export      Switch to the local defaults for the special characters.  The local default characters are
                            those of the local terminal at the time when telnet was started.

                import      Switch to the remote defaults for the special characters.  The remote default characters
                            are those of the remote system at the time when the TELNET connection was established.

                ?           Prints out help information for the slc command.

     status     Show the current status of telnet.  This includes the peer one is connected to, as well as the current
                mode.

     toggle arguments [...]
                Toggle (between TRUE and FALSE) various flags that control how telnet responds to events.  These flags
                may be set explicitly to TRUE or FALSE using the set and unset commands listed above.  More than one
                argument may be specified.  The state of these flags may be interrogated with the display command.
                Valid arguments are:

                authdebug     Turns on debugging information for the authentication code.

                autoflush     If autoflush and localchars are both TRUE, then when the ao or quit characters are rec-
                              ognized (and transformed into TELNET sequences; see set above for details), telnet
                              refuses to display any data on the user's terminal until the remote system acknowledges
                              (via a TELNET TIMING MARK option) that it has processed those TELNET sequences.  The
                              initial value for this toggle is TRUE if the terminal user had not done an "stty
                              noflsh", otherwise FALSE (see stty(1)).

                autodecrypt   When the TELNET ENCRYPT option is negotiated, by default the actual encryption (decryp-
                              tion) of the data stream does not start automatically.  The autoencrypt (autodecrypt)
                              command states that encryption of the output (input) stream should be enabled as soon as
                              possible.

                autologin     If the remote side supports the TELNET AUTHENTICATION option TELNET attempts to use it
                              to perform automatic authentication.  If the AUTHENTICATION option is not supported, the
                              user's login name are propagated through the TELNET ENVIRON option.  This command is the
                              same as specifying a option on the open command.

                autosynch     If autosynch and localchars are both TRUE, then when either the intr or quit character
                              is typed (see set above for descriptions of the intr and quit characters), the resulting
                              TELNET sequence sent is followed by the TELNET SYNCH sequence.  This procedure should
                              cause the remote system to begin throwing away all previously typed input until both of
                              the TELNET sequences have been read and acted upon.  The initial value of this toggle is
                              FALSE.

                binary        Enable or disable the TELNET BINARY option on both input and output.

                inbinary      Enable or disable the TELNET BINARY option on input.

                outbinary     Enable or disable the TELNET BINARY option on output.

                crlf          If this is TRUE, then carriage returns will be sent as <CR><LF>.  If this is FALSE, then
                              carriage returns will be send as <CR><NUL>.  The initial value for this toggle is FALSE.

                crmod         Toggle carriage return mode.  When this mode is enabled, most carriage return characters
                              received from the remote host will be mapped into a carriage return followed by a line
                              feed.  This mode does not affect those characters typed by the user, only those received
                              from the remote host.  This mode is not very useful unless the remote host only sends
                              carriage return, but never line feeds.  The initial value for this toggle is FALSE.

                debug         Toggles socket level debugging (useful only to the superuser).  The initial value for
                              this toggle is FALSE.

                encdebug      Turns on debugging information for the encryption code.

                localchars    If this is TRUE, then the flush, interrupt, quit, erase, and kill characters (see set
                              above) are recognized locally, and transformed into (hopefully) appropriate TELNET con-
                              trol sequences (respectively ao, ip, brk, ec, and el; see send above).  The initial
                              value for this toggle is TRUE in ''old line by line'' mode, and FALSE in ''character at
                              a time'' mode.  When the LINEMODE option is enabled, the value of localchars is ignored,
                              and assumed to always be TRUE.  If LINEMODE has ever been enabled, then quit is sent as
                              abort, and eof and suspend are sent as eof and susp (see send above).

                netdata       Toggles the display of all network data (in hexadecimal format).  The initial value for
                              this toggle is FALSE.

                options       Toggles the display of some internal telnet protocol processing (having to do with
                              TELNET options).  The initial value for this toggle is FALSE.

                prettydump    When the netdata toggle is enabled, if prettydump is enabled the output from the netdata
                              command will be formatted in a more user readable format.  Spaces are put between each
                              character in the output, and the beginning of any TELNET escape sequence is preceded by
                              a '*' to aid in locating them.

                skiprc        When the skiprc toggle is TRUE, TELNET skips the reading of the .telnetrc file in the
                              user's home directory when connections are opened.  The initial value for this toggle is
                              FALSE.

                termdata      Toggles the display of all terminal data (in hexadecimal format).  The initial value for
                              this toggle is FALSE.

                verbose_encrypt
                              When the verbose_encrypt toggle is TRUE, telnet prints out a message each time encryp-
                              tion is enabled or disabled.  The initial value for this toggle is FALSE.

                ?             Displays the legal toggle commands.

     z          Suspend telnet.  This command only works when the user is using the csh(1).

     ! [command]
                Execute a single command in a subshell on the local system.  If command is omitted, then an interac-
                tive subshell is invoked.

     ? [command]
                Get help.  With no arguments, telnet prints a help summary.  If a command is specified, telnet will
                print the help information for just that command.

ENVIRONMENT
     telnet uses at least the HOME, SHELL, DISPLAY, and TERM environment variables.  Other environment variables may
     be propagated to the other side via the TELNET ENVIRON option.

FILES
     ~/.telnetrc  user customized telnet startup values

HISTORY
     The telnet command appeared in 4.2BSD.

NOTES
     On some remote systems, echo has to be turned off manually when in ''old line by line'' mode.

     In ''old line by line'' mode or LINEMODE the terminal's eof character is only recognized (and sent to the remote
     system) when it is the first character on a line.

     Source routing is not supported yet for IPv6.

BSD                            February 3, 1994                            BSD